Semiconductor light emitting diode (LED) has become a promising device for general-purpose illumination applications. LEDs features include, excellent durability, long operation life, low power consumption, containing no mercury and potentially high efficiency. White LED is an illumination light source that is good for environmental protection and energy saving. Recently, LEDs are progressively being used in the illumination field for the electronic devices. For example, LEDs are popularly used in the mobile phones, personal digital assistants (PDAs) and so on.
Currently, the white LED adopts a red LED chip, a green LED chip and a blue LED chip to pack together in a packing structure so as to mix the three colors to form the white light.
Additionally, the color rendering index (Ra) is a measure of the ability of a light source to reproduce the colors of various objects being lit by the source. A high color rendering index light source can provide a better color representation for the object, that is, close to the natural color thereof. However, the color rendering index of a conventional LED is very poor. For example, the color rendering index of the conventional LED with red, blue and green LED chips is about 60˜70. Therefore, there is a need to improve the color rendering index for the LED illumination device.